Method and system for detecting capture using a coronary vein electrode

ABSTRACT

A method and device provide for determining capture in multiple chambers of a patient&#39;s heart using an electrode inserted into a coronary vein of the patient&#39;s heart. The coronary vein electrode is positioned adjacent to multiple heart chambers and is responsive to cardiac signals originating in the multiple chambers. The coronary vein electrode may be coupled to a single sense amplifier to detect the cardiac signals. Pace pulses may be applied to multiple heart chambers simultaneously or according to a phased timing sequence. Cardiac signals responsive to the pace pulses sensed using the coronary vein electrode may be used to verify capture in the multiple chambers of the heart.

RELATED PATENT DOCUMENT

This application is a division of U.S. patent application Ser. No.10/278,732 filed on Oct. 23, 2002, which is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates generally to implantable medical devicesand, more particularly, to verifying capture in multiple chambers of theheart using one or more electrodes positioned in a coronary vein of theheart.

BACKGROUND OF THE INVENTION

Rhythmic contractions of a healthy heart are normally controlled by thesinoatrial (SA) node, specialized cells located in the superior rightatrium. The SA node is the normal pacemaker of the heart, typicallyinitiating 60-100 heart beats per minute. When the SA node is pacing theheart normally, the heart is said to be in normal sinus rhythm (NSR).

A heart rhythm that deviates from normal sinus rhythm is an arrhythmia.Arrhythmia is a general term used to describe heart rhythm disturbancesarising from a variety of physical conditions and disease processes.Bradycardia occurs when the heart rhythm is too slow and has a number ofetiological sources including tissue damage due to myocardialinfarction, exposure to toxins, electrolyte disorders, infection, drugeffects, hypoglycemia or hypothyroidism. Bradycardia also may be causedby sick sinus syndrome, wherein the SA node loses its ability togenerate or transmit an action potential to the atria.

Supraventricular arrhythmias originate in the atria or surroundingtissues (vena cavae, pulmonary veins, etc.) resulting in a rapid-atrialrate. One mechanism for supraventricular tachycardia is an accessorypathway between the ventricular and atrial tissue. The accessorypathway, in combination with the normal AV nodal pathway, forms aconducting loop that can support reentry. The reentrant wave circulatesthrough the pathway and elevates the heart rate. Atrial flutter isanother type of supraventricular arrhythmia and arises when anelectrical wavefront circulates around an anatomical or functionalobstacle in the atrial myocardium. Atrial fibrillation occurs whenelectrical impulses initiate in the atria at irregular intervals andusually at a rate of greater than 300 impulses per minute. As a result,impulses reaching the AV node, and thus the ventricles, are alsoirregular, causing irregular contractions of the ventricles at anincreased rate.

Ventricular tachycardia occurs when impulses are initiated in theventricular myocardium with a rate more rapid than the intrinsic rate ofthe SA node. Ventricular tachycardia (VT) is characterized by a rapidheart beat and typically results from damage to the ventricularmyocardium from a myocardial infarction. Ventricular tachycardia canquickly degenerate into ventricular fibrillation (VF). Ventricularfibrillation is a condition denoted by extremely rapid, uncoordinatedcontractions of the ventricles. The rapid and erratic contractions ofthe ventricles degrades the ability of the ventricles to effectivelypump blood to the body and the condition is fatal unless the heart isreturned to sinus rhythm within a few minutes.

Implantable cardiac rhythm management (CRM) devices may incorporate bothdefibrillation and pacemaker circuitry used to treat patients withserious arrhythmias. CRM devices typically include circuitry to sensesignals from the heart and a pulse generator for providing electricalstimulation to the heart. Leads extending into the patient's heart areconnected to electrodes that contact the myocardium for sensing theheart's electrical signals and for delivering stimulation to the heartin accordance with various therapies for treating the arrhythmiasdescribed above.

Pacemakers deliver low energy electrical pace pulses timed to assist theheart in producing a contractile rhythm that maintains cardiac pumpingefficiency. Pace pulses may be intermittent or continuous, depending onthe needs of the patient. Defibrillators apply one or more high energypulses to the heart to terminate a tachyarrhythmia by shocking the heartinto a normal rhythm.

There exist a number of categories of pacemaker devices, with variousmodes for sensing and pacing the heart. Single chamber pacemakers paceand sense one heart chamber. Dual chamber pacemakers may pace and sensetwo chambers of the heart. Standard dual chamber pacemakers includeelectrodes positioned in the right atrium and right ventricle to provideatrial and ventricular pacing. In cardiac resynchronization devices, amultichamber pacemaker may include electrodes positioned to contactcardiac tissue within or adjacent to both the left and the rightventricles for pacing both the left and right ventricles. This type ofdevice allows bi-ventricular pacing therapy to be applied, for example,to coordinate ventricular contractions when a patient suffers fromcongestive heart failure (CHF). Furthermore, a pacemaker may includeelectrodes positioned to contact tissue within or adjacent to both theleft and the right atria to enable bi-atrial pacing. Bi-atrial pacingtherapy may be used, for example, to control atrial tachyarrhythmias.Future devices may pace different combinations of the four chambers oreven multiple sites within the same chamber to achieve optimalcoordination of contraction, arrhythmia suppression, or control ofcardiac remodeling.

When a pace pulse produces a contractile response in a heart, thecontractile response is typically referred to as capture, and theelectrical waveform corresponding to capture is denoted an evokedresponse. A pace pulse must exceed a minimum energy value, denoted thecapture threshold, to produce a contraction. Pacing therapy applied tomultiple sites on the heart, such as the bi-ventricular or bi-atrialpacing therapies discussed above, produces a change in the temporalcontraction pattern. When a pacing pulse is closely coupled to intrinsiccardiac electrical activity, the result is fusion. The evoked responsefrom fusion beats may be confused with either capture or noncapturedepending on the coupling interval between the intrinsic and pacedelectrical waveforms.

It is desirable for a pace pulse to have sufficient energy to produce acontractile response in the heart chambers stimulated without expendingenergy in excess of the capture threshold. Accurate detection of thecapture threshold is required for efficient pace energy management. Ifthe pace pulse energy is too low, the pace pulses may not reliablyproduce a contractile response in the heart resulting in ineffectivepacing. If the pace pulse energy is too high, the result may be patientdiscomfort as well as shorter battery life.

Capture detection, including fusion management, allows the cardiacrhythm management system to verify whether capture occurs in thestimulated heart chamber or chambers following a pacing pulse. Inparticular, capture detection for multiple heart chambers may be used inconjunction with bi-ventricular, bi-atrial pacing, or multisite pacingtherapies. If loss of capture is detected, the cardiac rhythm managementsystem may deliver a back-up pulse at a higher energy level to ensurecapture and subsequently initiate a threshold test to reset the pacingoutput to a safe level.

SUMMARY OF THE INVENTION

For the reasons stated above, and for other reasons stated below whichwill become apparent to those skilled in the art upon reading thepresent specification, there is a need in the art for a method anddevice that reliably and accurately detects capture in multiple chambersof a patient's heart using a minimum number of electrodes and associatedcircuitry. Various embodiments of the invention involve a system andmethod for verifying capture in a patient's heart when multi-chamberpacing therapies, such as bi-ventricular or bi-atrial pacing therapies,are applied to the heart.

According to one aspect of the invention, a coronary vein (CV) electrodeis positioned in a coronary vein adjacent to multiple heart chambers.Capture of multiple chambers responsive to simultaneous or phasedstimulation pulses may be detected by sensing an evoked response at thecoronary vein electrode. The evoked response will be a composite of theelectrical activity generated by the individual stimuli. The pattern ofelectrical activation, and therefore the composite evoked response, willdepend on whether capture occurs at individual sites. The differences inthe composite evoked response signal may be used to detect loss ofcapture at the individual pacing sites.

In accordance with an embodiment of the invention, a method fordetecting capture in multiple chambers of a patient's heart involvessensing, at a location in the coronary venous system of the patient'sheart, a cardiac signal responsive to stimulation signals applied tomultiple chambers of the patient's heart. The method further involvesdetermining if capture occurs in each of the cardiac chambers using thesignal sensed at the location in the coronary venous system.

Another embodiment of the invention provides a body implantable deviceincluding a lead system, a detector coupled to the lead system, and acontrol circuit coupled to the detector system. The lead system includesa coronary vein electrode and one or both of ventricular electrodes andatrial electrodes. The lead system conducts stimulation signals to apatient's heart. The sensing circuit includes a coronary vein senseamplifier that receives a cardiac signal sensed by the coronary veinelectrode in response to the stimulation signals. The detector circuituses the cardiac signal to determine if capture at each pacing siteoccurs.

In yet another embodiment of the invention, a system for detectingcapture in multiple chambers of a patient's heart includes means forsensing, at a location in the coronary venous system of the patient'sheart, a cardiac signal in response to multiple stimulation signalsapplied to the patient's heart and means for determining if captureoccurs at each stimulation site using the sensed cardiac signal.

The above summary of the present invention is not intended to describeeach embodiment or every implementation of the present invention.Advantages and attainments, together with a more complete understandingof the invention, will become apparent and appreciated by referring tothe following detailed description and claims taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial view of one embodiment of an implantable medicaldevice with an endocardial lead system extending into the heart withelectrodes positioned at multiple locations of the heart which caninclude locations in two or more of the left atrium, left ventricle,right atrium, right ventricle, the superior vena cava and the coronarysinus;

FIG. 2 is a system block diagram of an implantable medical device withwhich capture verification of the present invention may be implemented;

FIG. 3 is a number of graphs illustrating evoked response waveformssensed using a coronary sinus electrode in accordance with an embodimentof the invention;

FIG. 4 is a graph illustrating various implementations of capturedetection in accordance with an embodiment of the invention;

FIG. 5 is a flowchart illustrating a method of detecting capture inmultiple heart chambers in accordance with an embodiment of the presentinvention;

FIG. 6 is a flowchart illustrating a method of detecting capture inmultiple heart chambers using an maximum amplitude in a time window of acardiac signal sensed at a coronary vein electrode in accordance with anembodiment of the invention;

FIG. 7 is a flowchart illustrating a method of detecting capture inmultiple heart chambers using one or more features of a cardiac signalsensed at a coronary vein electrode in accordance with an embodiment ofthe invention;

FIG. 8 is a flowchart illustrating a method of detecting capture inmultiple heart chambers by comparing an evoked response template to acardiac signal sensed at a coronary vein electrode in accordance with anembodiment of the invention;

FIG. 9 is a flowchart illustrating a method of creating a feature setrepresentative of an evoked response for individual heart chambers inaccordance with an embodiment of the invention;

FIG. 10 is a flowchart illustrating a method of creating a feature setrepresentative of an evoked response for multiple heart chambers inaccordance with an embodiment of the invention;

FIG. 11 is a flowchart illustrating a method of performing anautocapture threshold test in accordance with an embodiment of theinvention;

FIG. 12 is a flowchart illustrating a method of performing beat-by-beatmonitoring of pacing in accordance with an embodiment of the invention;

FIG. 13 is a graph of cardiac signals sensed at a coronary veinelectrode during an atrial capture threshold test in accordance with anembodiment of the invention; and

FIG. 14 is a graph of cardiac signals sensed at a coronary veinelectrode during a biventricular capture threshold test in accordancewith an embodiment of the invention.

While the invention is amenable to various modifications and alternativeforms, specifics thereof have been shown by way of example in thedrawings and will be described in detail below. It is to be understood,however, that the intention is not to limit the invention to theparticular embodiments described. On the contrary, the invention isintended to cover all modifications, equivalents, and alternativesfalling within the scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

In the following description of the illustrated embodiments, referencesare made to the accompanying drawings which form a part hereof, and inwhich is shown by way of illustration, various embodiments in which theinvention may be practiced. It is to be understood that otherembodiments may be utilized, and structural and functional changes maybe made without departing from the scope of the present invention.

In general, pacing pulses may be applied to any of the heart chambers invarious combinations, depending on the type of therapy required. Pacingpulses may be applied simultaneously or phased in sequence to two ormore pacing sites. For example, patients suffering from chronic heartfailure may benefit from therapy including phased or simultaneous pacingpulses applied to both the left and right ventricles to coordinate theventricular contractions. Furthermore, it has been shown thatsynchronously pacing the left and right atria may prevent atrialfibrillation.

In modern cardiac rhythm management systems, the pacing stimulationenergy is typically a programmable parameter that may be adjusted toconform to a patient's needs. It is generally desirable to pace theheart using the lowest stimulation energy that reliably produces acontractile response. Pacing at an energy level that captures the heartwithout expending excess energy promotes patient comfort and lengthensbattery life.

A patient's capture threshold may change over time, and some advancedpacemakers are capable of periodically assessing a patient's capturethreshold through an autocapture procedure. Autocapture pacemakersperform an automated threshold test by ramping down the stimulationenergy applied to the heart until a loss of capture is detected. Theoptimum pacing stimulation may then be selected as the lowest pacingenergy reliably generating capture plus a reasonable margin of safety.

When the heart contracts following a pace pulse, capture occurs and acardiac signal, denoted the evoked response, is produced. The presenceof an evoked response may be used to determine if a particular pacepulse produced a heart contraction. An evoked response may be detectedby monitoring the pace pulses and examining the electrical signalsfollowing the pace pulses for indications of a contractile response.

When pacing and sensing from the same electrode, the evoked response maybe difficult to detect and identify because the evoked response may bevery small in contrast to the immediately preceding pace pulse. Inaddition, the evoked response may be obscured by lead polarizationeffects that occur after a pace pulse. Lead polarization is caused byelectrochemical reactions occurring where the electrode contacts thesurrounding aqueous medium. Lead polarization produces a pacing artifactafterpotential characterized by a large electrical signal immediatelyfollowing a pace pulse. The pacing artifact may be several times largerthan the evoked response. Capture detection may require additionalcircuitry or sensors used to sense the evoked response, therebyincreasing the complexity and cost of a device, particularly whencapture detection is required in multiple heart chambers or at multiplepacing sites.

The embodiments of the present system illustrated herein are generallydescribed as being implemented in a cardiac rhythm management (CRM)device incorporating a pacemaker that may operate in numerous pacingmodes known in the art. The present invention provides a system andmethod for verifying capture following pace pulses delivered to multipleheart chambers. Capture detection is implemented using an electrodelocated adjacent to multiple heart chambers and sensing the cardiacsignals responsive to pace pulses delivered to the multiple heartchambers. The use of a single sensing vector to detect capture inmultiple chambers reduces the complexity and cost of the CRM device. Thesystems and methods of the present invention may be implemented in CRMdevices that pace the heart and sense cardiac activity, such asimplantable cardioverters/defibrillators pacemakers, cardiacresynchronization devices, cardiac monitors, remote patient managementsystems, and device programmers, for example.

Capture verification in multiple chambers or at multiple pacing sitesmay be used to determine the optimal energy of the pace pulses deliveredto the multiple chambers. Additionally, capture verification may be usedto control back up pacing initiated when pace pulses delivered to theheart fail to evoke a contractile response. These and other applicationsmay be enhanced by employment of the systems and methods of the presentinvention.

In one embodiment, a CRM device configured as a dual chamberdefibrillator and pacemaker operates to detect capture in accordancewith the principles of the present invention. Various types of multiplechamber CRM devices are known in the art and may be used to implement acapture verification methodology of the present invention. Although thepresent system is described in conjunction with a CRM device having amicroprocessor-based architecture, it will be understood that the CRMdevice may be implemented in any logic-based architecture, if desired.

Referring now to FIG. 1 of the drawings, there is shown one embodimentof a medical device system which includes a CRM device 100 electricallyand physically coupled to an intracardiac lead system 102. Theintracardiac lead system 102 is implanted in a human body with portionsof the intracardiac lead system 102 inserted into a heart 101. Theintracardiac lead system 102 is used to detect and analyze electriccardiac signals produced by the heart 101 and to provide electricalenergy to the heart 101 under certain predetermined conditions to treatcardiac arrhythmias.

The intracardiac lead system 102 includes one or more electrodes usedfor pacing, sensing, or defibrillation. In the particular embodimentshown in FIG. 1, the intracardiac lead system 102 includes a rightventricular lead system 104, a right atrial lead system 105, and a leftatrial/ventricular lead system 106. In one embodiment, the rightventricular lead system 104 is configured as an integrated bipolarpace/shock lead.

The right ventricular lead system 104 includes an SVC-coil 116, anRV-coil 114, and an RV-tip electrode 112. The RV-coil 114, which mayalternatively be configured as an RV-ring electrode, is spaced apartfrom the RV-tip electrode 112, which is a pacing electrode for the rightventricle.

The right atrial lead system 105 includes a RA-tip electrode 156 and anRA-ring electrode 154. The RA-tip 156 and RA-ring 154 electrodes mayprovide respectively pacing pulses to the right atrium of the heart anddetect cardiac signals from the right atrium. In one configuration, theright atrial lead system 105 is configured as a J-lead.

In this configuration, the intracardiac lead system 102 is shownpositioned within the heart 101, with the right ventricular lead system104 extending through the right atrium 120 and into the right ventricle118. In particular, the RV-tip electrode 112 and RV-coil electrode 114are positioned at appropriate locations within the right ventricle 118.The SVC-coil 116 is positioned at an appropriate location within theright atrium chamber 120 of the heart 101 or a major vein leading to theright atrium chamber 120 of the heart 101. The RV-coil 114 and SVC-coil116 depicted in FIG. 1 are defibrillation electrodes.

The left atrial/left ventricular lead system 106 includes a coronaryvein (CV) electrode 126 positioned within a coronary vein of the heart101 and adjacent multiple heart chambers. The CV electrode 126 may belocated, for example, in the coronary sinus 150 of the heart andadjacent to one or more heart chambers for detecting cardiac signalsoriginating in one or more heart chambers. Additionally, oralternatively, one or more coronary vein electrodes may be positioned ina middle cardiac vein, a left posterior vein, a left marginal vein, agreat cardiac vein or an anterior vein.

An LV-tip electrode 113, and an LV-ring electrode 117 are insertedthrough the coronary venous system and positioned adjacent to the leftventricle 124 of the heart 101. The LV-ring electrode 117 is spacedapart from the LV-tip electrode 113, which is a pacing electrode for theleft ventricle. The LV-tip 113 and LV-ring 117 electrodes may also beused for sensing the left ventricle. The left atrial/left ventricularlead system 106 further includes an LA-tip 136 and LA-ring 134 electrodepositioned adjacent the left atrium 122 for pacing and sensing the leftatrium 122 of the heart 101.

The left atrial/left ventricular lead system 106 includes endocardialpacing leads that are advanced through the superior vena cava (SVC), theright atrium 120, the valve of the coronary sinus, and the coronarysinus 150 to locate the LA-tip 136, LA-ring 134, LV-tip 113 and LV-ring117 electrodes at appropriate locations adjacent to the left atrium andventricle 122, 124, respectively. In one example, leftatrial/ventricular lead placement involves creating an opening in apercutaneous access vessel, such as the left subclavian or left cephalicvein. The left atrial/left ventricular lead 106 is guided into the rightatrium 120 of the heart via the superior vena cava.

From the right atrium 120, the left atrial/left ventricular lead system106 is deployed into the coronary sinus ostium, the opening of thecoronary sinus 150. The lead system 106 is guided through the coronarysinus 150 to a coronary vein of the left ventricle 124. This vein isused as an access pathway for leads to reach the surfaces of the leftatrium 122 and the left ventricle 124 which are not directly accessiblefrom the right side of the heart. Lead placement for the leftatrial/left ventricular lead system 106 may be achieved via thesubclavian vein access and a preformed guiding catheter for insertion ofthe LV and LA electrodes 113, 117, 136, 134 adjacent the left ventricle124 and left atrium 122, respectively. In one configuration, the leftatrial/left ventricular lead system 106 is implemented as a single-passlead.

The CV electrode 126 may be positioned in the proximity of the AV groovein such a way as to lie in the proximity of multiple heart chambers. Thecoronary vein electrode 126 may be located in one of a coronary sinus150, a middle cardiac vein, a left posterior vein, a left marginal vein,a great cardiac vein or an anterior vein of the patient's heart 101. TheCV electrode 126 may be configured as a coil electrode. Alternately, oneor more small band electrodes may be positioned in the coronary sinus150 adjacent to one or more heart chambers 120, 118, 122, 124.

Referring now to FIG. 2, there is shown an embodiment of a CRM device200 suitable for implementing a capture verification methodology of thepresent invention. FIG. 2 shows a CRM device divided into functionalblocks. There exist many possible configurations in which thesefunctional blocks can be arranged. The example depicted in FIG. 2 is onepossible functional arrangement. The CRM device 200 includes circuitryfor receiving cardiac signals from a heart 101 (not shown in FIG. 2) anddelivering electrical energy in the form of pace pulses orcardioversion/defibrillation pulses to the heart.

The right ventricular lead system includes conductors 102 and 104 fortransmitting sense and pacing signals between terminals 202 and 204 ofthe CRM device and the RV-tip and RV-coil electrodes, respectively. Theright ventricular lead system further includes conductor 101 fortransmitting signals between the SVC coil and terminal 201 of the CRMdevice 200. The right atrial lead system includes conductor 106 fortransmitting signals between the RA-tip electrode and terminal 206 andconductor 108 for transmitting signals between the RA-ring electrode andterminal 208.

The left atrial/ventricular lead system includes conductors 110, 112 fortransmitting sense and pacing signals between terminals 210, 212 of theCRM device 200 and LV-tip and LV-ring electrodes respectively. The leftatrial/ventricular lead system also includes conductor 118 fortransmitting sense signals between terminal 218 of the CRM device 200and the CV electrode. A can electrode 209 coupled to a housing 130 ofthe CRM device 200 is also provided.

In one embodiment, the CRM device circuitry 203 is encased in ahermetically sealed housing 130 suitable for implanting in a human body.Power to the CRM device 200 is supplied by an electrochemical battery233 that is housed within the CRM device 200. In one embodiment, the CRMcircuitry 203 is a programmable microprocessor-based system, including acontrol system 220, detector system 230, pacemaker 240,cardioverter/defibrillator pulse generator 250 and a memory circuit 261.The memory circuit 261 stores parameters for various pacing,defibrillation, and sensing modes and stores data indicative of cardiacsignals received by other components of the CRM circuitry 203. A memoryis also provided for storing historical EGM and therapy data 262, whichmay be used on-board for various purposes and transmitted to an externalprogrammer unit 280 as required.

The control system 220 may use various control subsystems includingpacemaker control 221, cardioverter/defibrillator control 224, capturedetector 223, and arrhythmia detector 222. The control system 220 mayencompass additional functional components (not shown) for controllingthe CRM circuitry 203. The control system 220 and memory circuit 261cooperate with other components of the CRM circuitry 203 to performoperations involving capture verification according to the principles ofthe present invention, in addition to other sensing, pacing anddefibrillation functions.

Telemetry circuitry 270 is additionally coupled to the CRM circuitry 203to allow the CRM device 200 to communicate with an external programmerunit 280. In one embodiment, the telemetry circuitry 270 and theprogrammer unit 280 use a wire loop antenna and a radio frequencytelemetric link to receive and transmit signals and data between theprogrammer unit 280 and telemetry circuitry 270. In this manner,programming commands may be transferred to the CRM circuitry 203 fromthe programmer unit 280 during and after implant. In addition, storedcardiac data pertaining to capture verification and capture threshold,along with other data, may be transferred to the programmer unit 280from the CRM device 200, for example.

Cardiac signals derived from the right ventricle may be detected as avoltage developed between the RV-tip electrode and the RV-coil in abipolar sensing configuration. RV-tip and RV-coil electrodes are showncoupled to an RV-sense amplifier 231 located within the detector system230. Rate channel signals received by the RV-sense amplifier 231 arecommunicated to the signal processor and A/D converter 239. The RV-senseamplifier 231 serves to sense and amplify the rate channel signals. Thesignal processor and A/D converter 239 convert the R-wave signals fromanalog to digital form and communicate the signals to the control system220.

Signals derived from the right ventricle may also be detected as avoltage developed between the RV-tip electrode and the can electrode209. Cardiac signals may also be detected as a voltage developed betweenthe RV-coil and the SVC-coil coupled to the can electrode 209. Signalsdeveloped using appropriate combinations of the RV-coil, SVC-coil, andcan electrode 209 are sensed and amplified by a shock EGM amplifier 236located in the detector system 230. The output of the EGM amplifier 236is coupled to the control system 220 via the signal processor and A/Dconverter 239.

Signals derived from the left ventricle may be detected as a voltagedeveloped between the LV-tip electrode and the LV-ring electrode in abipolar sensing configuration. LV-tip and LV-ring electrodes are showncoupled to an LV-sense amplifier 233 located within the detector system230. Signals received by the LV-sense amplifier 233 are communicated tothe signal processor and A/D converter 239. The LV-sense amplifier 233serves to sense and amplify the signals. The signal processor and A/Dconverter 239 convert the R-wave signals from analog to digital form andcommunicate the signals to the control system 220.

Although the embodiment described in the paragraph above involves abipolar sensing configuration, unipolar sensing is also possible. Inunipolar sensing, signals derived from the left ventricle may bedetected as a voltage developed between the LV-tip electrode or theLV-ring electrode and the can electrode 209, for example. These unipolarsignals may be appropriately sensed and amplified similarly to themethod described for the bipolar sensing configuration illustrated inFIG. 2.

RA-tip and RA-ring electrodes are shown coupled to an RA-sense amplifier232 located within the detector system 230. Atrial sense signalsreceived by the RA-sense amplifier 232 in the detector system 230 arecommunicated to an A/D converter 239. The RA-sense amplifier serves tosense and amplify the A-wave signals of the right atrium. The A/Dconverter 239 converts the sensed signals from analog to digital formand communicates the signals to the control system 220.

A-wave signals originating in the left atrium are sensed by the LA-tipand LA-ring electrodes. The A-waves are sensed and amplified by theLA-sense amplifier 234 located in the detector system. The LA-senseamplifier serves to sense and amplify the A-wave signals of the leftatrium. The A/D converter 239 converts the sensed signals from analog todigital form and communicates the signals to the control system 220.

Alternatively, unipolar atrial sense signals may be derived fromvoltages developed between the RA-tip, RA-ring, LA-tip or LA-ringelectrodes and the can electrode 209. These unipolar signals may beappropriately sensed and amplified similarly to the method described forthe bipolar sensing configuration illustrated in FIG. 2.

The pacemaker 240 communicates pacing signals to the pacing electrodes,RV-tip, RA-tip, LV-tip and LA-tip, according to a pre-established pacingregimen under appropriate conditions. Blanking circuitry (not shown) isemployed in a known manner when ventricular or atrial pacing pulses aredelivered, such that the ventricular channels, atrial channels, andshock channel are properly blanked at the appropriate time and for theappropriate duration.

Far-field and/or near-field signals developed between the CV-coil andcan electrode 209 are used to detect the evoked response (ER) followinga pace pulse applied to any heart chamber or any combination of theheart chambers. The CV-coil and can electrode 209 are coupled through anER amplifier 235 to the signal processor and A/D converter 239 locatedin the detector system 230. The ER amplifier serves to sense and amplifythe evoked response signals. The A/D converter 239 converts the sensedsignals from analog to digital form and communicates the signals to thecontrol system 220. The ER signals are coupled to capture detectorcircuitry 223 within the control system 220.

The output of the capture detector circuitry 223 communicates with thepacemaker control 221 for control of backup pacing. If an evokedresponse is not detected following a pace pulse, the pacemaker control221 may initiate a back-up pace pulse.

As previously discussed, one or more electrodes inserted in the coronarysinus or in other locations accessible through the coronary venoussystem may be positioned adjacent to one or more chambers of the heart.An evoked response signal sensed by the coronary vein electrode may beused to detect capture in any of the four heart chambers individually,or in multiple heart chambers following simultaneous or phased pacepulses. An evoked response signal may be generated by delivering a pacepulse to a single chamber or multiple chambers at a level higher thanthe capture threshold.

The morphology of an evoked response from any individual chamber or frommultiple chambers sensed at a coronary vein (CV) electrode is repeatableduring a specific time window following a pace pulse. FIG. 3 illustratesa representative evoked response signal 302 resulting from a leftventricle only pace pulse, and a representative evoked response signal303 resulting from a bi-ventricular pace pulse. Cardiac signals, such asthe evoked responses 302, 303 represented in the graphs of FIG. 3, aresensed at the coronary vein electrode, amplified in the ER amplifier,processed and digitized by the CRM detector circuitry, and presented tothe capture detector in the control system of the CRM device.

Capture detection may be implemented in the capture detector 223, shownin FIG. 2, using various techniques. In one embodiment, the capturedetector determines capture has occurred by comparing an amplitude ofthe sensed cardiac signal within a specified time window following thestimulation pulse to an amplitude associated with an evoked response. Ifthe sensed cardiac signal achieves the amplitude associated with theevoked response, indicating capture of multiple chambers, the capturedetector determines that capture has occurred. Furthermore, the capturedetector may detect various features of a cardiac waveform consistentwith a given evoked response morphology to determine if capture occursat each pacing site. An exemplary set of features that may be used todetermine capture include a slope of the cardiac signal, timing of localmaxima or minima of the cardiac signal, the rise time and/or fall timesof the cardiac signal, or a curvature of the cardiac signal. Otherfeatures of the cardiac signal may also be used to determine capture.Furthermore, one or more time intervals between cardiac signal featuresmay also be used to determine capture.

Capture may also be determined by comparing a cardiac signal produced bya stimulus pulse and an evoked response template. The evoked responsetemplate is a representative evoked response waveform, sensed using thecoronary vein electrode, for the multiple chambers paced. Multipleevoked response templates may be created for each possible scenario. Forexample, evoked response templates may be created for right ventricularcapture, left ventricular capture, and biventricular capture inconventional biventricular pacing. By this method, a cardiac signalsensed at the CV electrode is sampled at a predetermined sample rate.All or a portion of the samples of the cardiac signal may be compared tocorresponding samples of the evoked response template. If the sensedcardiac signal is comparable to the evoked response template for anindividual chamber or multiple chambers, capture of the individual ormultiple chambers may be confirmed.

Multiple heart chambers may be paced synchronously or in phased timesequence to provide an appropriate therapy to the heart. When multiplechambers are paced, capture may occur in a single heart chamber,multiple heart chambers, or not at all. By the methods of the presentinvention, capture in a single chamber may be detected and discriminatedfrom multiple chamber capture. For example, bi-ventricular pacingincludes pacing both the right and the left ventricles. By the methodsof the present invention, the coronary vein electrode may be used todetect capture in the right ventricle only, the left ventricle only, orboth the left and the right ventricles in response to pacing pulsesapplied to the left and right ventricles in simultaneous or phased timesequence. The methods of the present invention may also be used todifferentiate between capture in multiple heart chambers and capture ina single heart chamber.

The implementations of capture detection discussed above are illustratedin FIG. 4. FIG. 4 is a graph of a cardiac signal produced bybi-ventricular stimulation. Capture may be verified, for example, bydetecting a predetermined signal amplitude, V_(BiV), that is indicativeof an evoked response within a specified time window following the pacepulses. The time window may begin at the application of the stimulationsignal and extend for a predetermined time interval. Alternatively, oradditionally, capture may be verified by comparing the time T_(max) of alocal extrema of the waveform to the timing of a bi-ventricular evokedresponse local extrema.

Capture may also be detected by when a positive slope of the waveform,Slope 1, or a negative slope of the waveform, Slope 2, achieves a valueassociated with an evoked response. Furthermore, capture may be detectedwhen a rise time, T_(Rise), of the cardiac signal between predeterminedsignal amplitudes, for-example, V_(R1) and V_(R2), is consistent withthe rise time of an evoked response. Capture may also be detected when acurvature of the cardiac signal is consistent with a curvaturecharacteristic of an evoked response.

The presence of one or more of the above cardiac signal features thatare consistent with the evoked response may be used to determinecapture. In addition, time intervals between two or more cardiac signalfeatures may be used to determine capture.

The morphology of the cardiac signal shown in FIG. 4 may vary dependingupon the number and identity of the heart chambers captured by the pacepulses. For example, the morphology of a cardiac signal resulting fromcapture of a single chamber will generally present a morphologydifferent from the morphology of a cardiac signal resulting from captureof multiple chambers. These differences in cardiac signal morphology maybe used to differentiate capture in multiple chambers from capture in asingle chamber.

A method for determining capture in multiple heart chambers according toan embodiment of the invention is illustrated in the flowchart of FIG.5. Stimulation signals are provided 510 to two or more heart chambers.The stimulation signals may be applied, for example, simultaneously orin accordance with an appropriate phased time sequence. The cardiacresponse following the stimulation signals is detected 520 using anelectrode inserted in the coronary venous system of the heart. Capturein the two or more chambers is determined 530 using the cardiac signalsensed by the coronary vein electrode.

As previously discussed, capture may be determined by sensing a cardiacsignal at the CV electrode following a pace pulse and comparing thecardiac signal in various ways to known evoked response waveforms at theCV electrode. In one example, capture may be detected when the cardiacsignal sensed at the CV electrode reaches a predetermined amplitudeindicative of an evoked response signal during a time window following apace pulse.

The flowchart of FIG. 6 illustrates a method of capture verification bycomparison of an amplitude consistent with an evoked response to theamplitude of a cardiac signal sensed at the CV electrode following apace pulse. According to this method, the characteristic amplitude of anevoked response of the multiple chambers sensed at the CV electrode isdetermined 610. A stimulus pulse is applied to the multiple heartchambers 620. The cardiac signal responsive to the stimulus pulse issensed using the CV electrode 630. The amplitude of the sensed cardiacsignal is measured within a predetermined time window following thestimulus pulse 640. If the amplitude of the cardiac signal is consistentwith the characteristic amplitude of an evoked response by the multipleheart chambers 650, capture is verified 660. If the amplitude of thecardiac signal is not consistent with the characteristic amplitude of anevoked response 650, a condition of non-capture is detected 670.

A cardiac signal may be characterized by a set of features taken fromthe signal waveform. An exemplary set of features that may be used tocharacterize a cardiac signal waveform include the slope of the waveformat particular coordinates, the rise time of the signal, or the time of alocal extrema of the cardiac signal waveform. Other features includingfirst and second derivatives, for example, may also be useful incharacterizing the waveform for capture detection.

Capture in one or multiple heart chambers may be determined by comparingfeatures of a cardiac signal detected at the CV electrode to featuresrepresentative of an evoked response waveform detected at the CVelectrode. The features of an evoked response waveform indicative ofcapture in a single heart chamber may be differentiated from thefeatures of an evoked response waveform indicative of capture inmultiple heart chambers. A number of evoked response waveformsindicative of capture may be acquired and averaged or otherwise combinedwith previously acquired features to update the features used torepresent an evoked response in the single or multiple heart chambers.

FIG. 7 illustrates a method of detecting capture by comparing thefeatures of an evoked response with the features of a cardiac signalresponsive to a stimulus pulse in accordance with an embodiment of theinvention. One or more features of a cardiac signal representative of anevoked response by two or more heart chambers are determined 710.Stimulation pulses are applied to two or more chambers of the heart 720.The cardiac signal responsive to the stimulation pulses is sensed at aCV electrode 730. Features of the cardiac signal are determined 740 andcompared to the features of an evoked response 750. If the features ofthe cardiac signal are consistent with features of an evoked response760, capture in the multiple chambers is detected 770. If the featuresof the cardiac signal are not consistent with features of an evokedresponse 760, capture is not detected 780.

A template characterizing an evoked response following pace pulsesapplied to the heart may be determined for each individual heart chamberand for multiple heart chambers. The templates may be used to verifycapture in an individual heart chamber or in multiple heart chambers.Thus, each individual heart chamber as well as multiple heart chambersmay be associated with an evoked response template. An evoked responsetemplate for an individual chamber or multiple chambers may bedetermined, for example, by delivering a pulse to each paced heartchamber or chambers at a voltage greater than the capture threshold. Ifmultiple chambers are paced, pace pulses may be applied simultaneouslyor closely phased in time to the paced heart chambers. An evokedresponse waveform produced by the high energy pulses may be stored foreach chamber and for multiple chambers as an initially determined evokedresponse template for the chamber or chambers. Additional evokedresponse waveforms for individual or multiple heart chambers may beproduced and averaged or otherwise combined with the initiallydetermined evoked response templates to update the templates. Capture inan individual chamber or in multiple chambers may be determined bycomparing the evoked response template for the chamber or chambers to acardiac signal sensed at the CV electrode following a pace pulse to thechamber or chambers.

A method for determining capture in multiple heart chambers bycomparison of a template to a cardiac waveform is illustrated in theflowchart of FIG. 8. An evoked response template is determined by pacingthe multiple heart chambers at an energy level higher than the capturethreshold. The cardiac signal resulting from the application of the highenergy pace pulses is detected using the CV electrode and stored as anevoked response template 810. The multiple chambers of the heart arepaced 820 and the responsive cardiac signal is sensed using the CVelectrode 830. Samples of the cardiac signal are compared to samples ofthe previously stored template 840. If the cardiac signal is comparableto the evoked response template 850, then capture in the multiplechambers is verified 860. If the cardiac signal is not comparable to theevoked response waveform 850, the stimulation pulse did not capture themultiple heart chambers and non-capture is verified 870.

The flowchart of FIG. 9 illustrates an example method for characterizingone or more cardiac signal features representative of an evoked responsefor a single heart chamber in accordance with an embodiment of theinvention. The feature set characterized by this method may be used todetect capture in the single heart chamber for subsequently applied pacepulses as previously discussed.

A heart chamber is selected for the feature characterization 910 and theselected chamber is paced 920 at high voltage. The pace voltage must behigh enough to capture the heart chamber and produce an evoked response.The evoked responses produced by the pace pulses may be analyzed andused to characterize a cardiac signal feature set representative of anevoked response.

The electrogram of the cardiac signal responsive to the high voltagepace pulse is sensed 930 using a coronary vein electrode arranged tosense cardiac signals in the selected chamber. One or more features areextracted 940 from the electrogram and stored. For example, the featuresextracted and stored may include a slope of the cardiac signal, a timingof local maxima or minima of the cardiac signal, the rise time and/orfall times of the cardiac signal, or a curvature of the cardiac signal.The processes of blocks 920-940 may be repeated until a predeterminednumber of pace pulses have been delivered 950 and the correspondingcardiac signals sensed. The stored features for each sensed cardiacsignal may be analyzed to determine if a subset of the beats, forexample, about 8 out of 10 beats, are comparable. If the features of thesubset of the total number of beats are comparable 960, then an evokedresponse feature set for capture detection is created 980 from thecomparable features for the chamber. The feature set may be used forcapture determination for the chamber. If the features of the subset ofthe total number of beats are not comparable 960, then a feature set forthe single chamber is not created 970.

The flowchart of FIG. 10 illustrates an example method forcharacterizing a feature set of one or more cardiac signal featuresrepresentative of an evoked response for multiple heart chambers inaccordance with an embodiment of the invention. The feature setcharacterized by this method may be used to detect capture in multiplechambers for pace pulses applied to the multiple chambers. The pacepulses may be applied to the heart chambers simultaneously or deliveredsequentially within a time period.

Two or more heart chambers are selected for feature characterization1010. The selected chambers are paced 1020 simultaneously or in closelyphased sequence at high voltage. Pacing at full voltage ensures captureof the multiple chambers and allows the characterization of a cardiacsignal feature set representative of an evoked response for the multiplechambers. An electrogram of the cardiac signal responsive to the highvoltage pace pulses applied to the multiple chambers is sensed 1030using a coronary vein electrode. The coronary vein electrode is arrangedadjacent to the multiple chambers and is capable of sensing cardiacsignals from the multiple chambers. One or more features may beextracted 1040 from the electrogram and stored. The process of blocks1020-1040 may be repeated until a predetermined number of pace pulses,for example N pulses, have been delivered 1050 and the correspondingcardiac signals sensed. The stored features for each sensed cardiacsignal may be analyzed to determine if a subset of the beats, forexample, about 8 out of 10 beats are comparable. If the features of thesubset of the total number of beats are not comparable 1060, then afeature set for the multiple chambers is not created 1070. If thefeatures of the subset of the total number of beats are comparable 1060,then a feature set for capture detection in the multiple chambers iscreated 1080. In addition, feature sets may be created 1090 for eachchamber individually in accordance with the process discussed above andillustrated in FIG. 9.

Periodic capture threshold adjustment may be necessary to maintaineffective pacing because the patient's capture threshold may vary overtime. A patient's capture threshold in an individual heart chamber or inmultiple heart chambers may be periodically assessed through anautocapture procedure initiated by the CRM device.

In accordance with an embodiment of the invention, an autocaptureprocedure may be performed for multiple heart chambers using cardiacsignals detected at a coronary vein electrode. The autocapture procedurefor multiple heart chambers may be implemented by ramping down thestimulation energy applied to the heart chambers until a loss of captureis detected in the multiple chambers.

At each stimulation energy, the cardiac signal following the pace pulseis detected and analyzed to determine if the sensed cardiac signalrepresents an evoked response. A particular stimulation energy may bedetermined to reliably produce capture if a predetermined percentage ofpace pulses at the particular stimulation energy produces an evokedresponse. The optimum pacing stimulation may then be selected as thelowest pacing energy reliably generating capture plus a reasonablemargin of safety.

FIG. 11 is a flowchart of a method for performing an autocaptureprocedure for determining the capture threshold of multiple heartchambers in accordance with principles of the invention. An initialfeature set is created 1105 for the multiple heart chambers involved inthe autocapture test. Characteristic feature sets for detecting capturein multiple or individual heart chambers may be created as discussedabove in connection with FIGS. 9 and 10.

The autocapture test may be performed by ramping down the pacing energyfrom an energy level that ensures capture to a level at which loss ofcapture is detected. The pacing output is initialized 1110 byprogramming the pacing output to the maximum pacing energy. Pacingstimulus pulses are delivered 1115 to the heart chambers at theprogrammed voltage. A cardiac signal responsive to the pacing pulse issensed 1117 using the coronary sinus electrode. Features of the sensedcardiac signal are extracted 1120 and compared 1125 to one or morefeatures of the characteristic evoked response feature sets for themultiple heart chambers.

If the features of the sensed cardiac signal are comparable 1125 to oneor more of the characteristic evoked response features, then capture isdetected 1155. Pace pulses at each programmed pacing voltage are appliedto the heart for a maximum number of beats to determine if theprogrammed pacing voltage repeatedly produces capture. If apredetermined number of beats at the programmed voltage produces capture1160, for example, about 3 captured beats out of 5 beats, then theprogrammed voltage is determined to reliably produce capture and thepacing voltage is decremented 1175. However, if the maximum number ofbeats at the programmed voltage are delivered 1165 without producing thepredetermined number of captured beats, the programmed voltage does notreliably produce capture 1167. The minimum capture voltage is determined1170 as the programmed voltage plus the step size.

The process of pacing the selected chambers at successively smallervoltages continues until a lowest capture voltage is determined, oruntil the programmed voltage falls below a minimum voltage 1180. If theminimum voltage is reached 1180 without detecting a pacing voltage thatreliably produces capture, no threshold is found 1185.

If a feature match is not detected 1125 between a cardiac signalproduced by a pace pulse and the characteristic features produced by anevoked response, a fusion detection process 1130 is initiated. Thecardiac signal is analyzed to determine 1130 if the cardiac beatrepresents a fusion beat. If the cardiac beat is a fusion beat, thenfusion management 1135 may be performed to modify the pacing parametersso that the incidence of fusion is reduced. If the fusion management isnot successful, and fusion beats continue to be detected 1140, theautocapture test is terminated 1145. If a feature match is not detected1125, and fusion is not detected 1130, loss of capture is determined1150. The lowest capture voltage is established as the programmedvoltage plus the step size 1152.

A process for beat-by-beat monitoring of pacing to ensure capture isillustrated in the flowchart of FIG. 12. The preceding discussionillustrates a method for performing an autocapture test for multipleheart chambers using cardiac signals sensed at a coronary sinuselectrode. The pacing voltage for the multiple chambers may beinitialized 1210 to the lowest capture voltage determined by the testplus some margin of safety. The multiple chambers are paced 1220 at theprogrammed voltage. The cardiac signal following each pace pulse issensed 1225 at the coronary sinus electrode. One or more features of thesensed cardiac signal are extracted 1230 and are compared to one or morefeatures characteristic of an evoked response. If the one or morefeatures are comparable 1240, capture of the multiple chambers isverified 1250 and pacing at the programmed voltage continues.

If the features of the sensed cardiac signal are not comparable 1240 tothe features characteristic of an evoked response, the cardiac signal isanalyzed to determine if the beat is a fusion beat. If the beat is afusion beat 1260, then fusion management processes are initiated 1295 toeliminate or reduce the incidence of fusion.

However, if the cardiac beat is not a fusion beat 1260, then a loss ofcapture determination is made 1270. The previous pace pulse did noteffectively produce a contractile response in the heart chambers. Inthis situation, back up pulses at a higher voltage are delivered 1275 tothe heart chambers.

If loss of capture is repeatedly detected 1280, for example, if about 2loss of capture episodes are detected in 3 beats, then the programmedpacing voltage may not reliably capture the heart chambers. The CRMbegins operating in safety mode 1285, wherein the heart is paced at ahigh voltage to reliably produce a captured response. A threshold testmay be scheduled 1290 to reassess the capture threshold for the multiplechambers.

FIGS. 13 and 14 are graphs of cardiac signals taken during an atrialcapture threshold test and a biventricular capture threshold test,respectively. The graphs labeled CV-Can represent cardiac signals sensedbetween a CV electrode located in the coronary sinus of the heart andthe CRM device can electrode. The CV electrode is positioned so that theCV electrode is adjacent to all four heart chambers. FIG. 13 is a graphof experimental data showing the cardiac signal sensed between CV andcan electrodes during an atrial capture threshold test. The atrialcapture threshold test steps down the pacing energy applied to the rightatrium until loss of capture is detected. As illustrated by the data ofFIG. 13, loss of capture is visible in the signals detected using the CVelectrode positioned in the coronary sinus. FIG. 14 shows theexperimental data acquired during a bi-ventricular capture thresholdtest. In this example, the CV-Can cardiac signal shows a loss of capturein the right ventricle only.

Various modifications and additions can be made to the preferredembodiments discussed above without departing from the scope of thepresent invention. Accordingly, the scope of the present inventionshould not be limited by the particular embodiments described above, butshould be defined only by the claims set forth below and equivalentsthereof.

1. A body implantable system, comprising: a lead system comprising acoronary vein electrode and one or more ventricular or atrialelectrodes, the lead system configured to deliver stimulation signals tomultiple chambers of a patient's heart via at least the one or moreventricular or atrial electrodes; a detector coupled to the lead system,the detector comprising a coronary vein sense amplifier configured toreceive a cardiac signal sensed by the coronary vein electrode followingthe one or more stimulation signals; and a control circuit coupled tothe detector, the control circuit configured to use the cardiac signalto detect capture of the multiple heart chambers.
 2. The system of claim1, wherein the coronary vein electrode is configured to be positioned inproximity of an AV groove of the patient's heart.
 3. The system of claim1, wherein the coronary vein electrode is configured to be located inone of a coronary sinus, a middle cardiac vein, a left posterior vein, aleft marginal vein, a great cardiac vein or an anterior vein of thepatient's heart.
 4. The system of claim 1, wherein: the lead system isconfigured to deliver simultaneous or sequential stimulation pulses tothe ventricles of the patient's heart; and the control circuit isconfigured to detect capture of the ventricles.
 5. The system of claim1, wherein: the lead system is configured to deliver simultaneous orsequential stimulation pulses to atria of the patient's heart; and thecontrol circuit is configured to detect capture of the atria.
 6. Thesystem of claim 1, wherein: the lead system is configured to deliverstimulation pulses to at least one ventricle and at least one atrium ofthe patient's heart; and the control circuit is configured to detectcapture of the at least one ventricle and the at least one atrium. 7.The system of claim 1, wherein the control circuit is configured tocompare the cardiac signal sensed by the coronary vein electrode to oneor more templates to detect capture.
 8. The system of claim 7, wherein:the one or more templates includes a bi-ventricular template; and thecontrol circuit is configured to detect capture of a right ventricle anda left ventricle of the patient's heart using the bi-ventriculartemplate.
 9. The system of claim 7, wherein: the one or more templatesincludes a bi-atrial template; and the control circuit is configured todetect capture of a right atrium and a left atrium of the patient'sheart using the bi-atrial template.
 10. The system of claim 7, whereinthe one or more templates includes a single template.
 11. The system ofclaim 7, wherein: the one or more templates includes a right heartchamber template and a left heart chamber template; and the controlcircuit is configured to detect capture of a right heart chamber usingthe right heart chamber template and to detect capture of a left heartchamber using the left heart chamber template.
 12. The system of claim7, wherein the control circuit is configured to generate or update theone or more templates using one or more evoked response signals.
 13. Thesystem of claim 1, wherein the control circuit is configured todetermine timing of local extrema of the sensed cardiac signal and todetect capture based on the timing of the local extrema.
 14. The systemof claim 1, wherein the control circuit is configured to determine atime interval between features of the sensed cardiac signal and todetect capture based on the time interval.
 15. The system of claim 1,wherein the control circuit is configured to differentiate betweencapture in multiple heart chambers and capture in a single heartchamber.
 16. The system of claim 1, wherein the control circuit isfurther configured to perform a threshold test to determine an optimalpacing energy for one or more heart chambers.
 17. The system of claim 1,wherein the control circuit is further configured to is analyze thecardiac signal to determine if a cardiac beat is a fusion beat.
 18. Thesystem of claim 17, wherein the control circuit is further configured toinitiate fusion management if the beat is a fusion beat.
 19. The systemof claim 18, wherein the fusion management comprises modification ofpacing parameters.
 20. The system of claim 1, wherein the cardiac signalis sensed using a CV electrode to can sensing vector.